1. Field of the Invention
The present invention relates to a tilt-adjustable motor vehicle seat of the type in which a backrest of the seat is connected with a seat part of the seat via bilateral articulations including a first articulation part secured stationarily on the seat, a second articulation part secured stationarily on the backrest, and a pivot axle disposed between and pivotally coupling the articulation parts together. More particularly, the present invention relates to a latching device for locking the backrest relative to the seat part in response to the motor vehicle exceeding a predetermined acceleration value acting in the longitudinal direction of the motor vehicle.
2. Description of the Prior Art
The articulations between a seat part of a motor vehicle seat and its backrest whose inclination can be adjusted relative to the seat part are implemented as inclination adjustment fittings. For the pure function of adjustment of the angle of inclination an adjustment fitting disposed on one of the sides of the seat is entirely sufficient. At normal vehicle acceleration or at normal seat loading through the passenger, this one adjustment fitting secures the backrest securely in the adjusted angle of inclination. In the event of a crash in which very high negative or positive accelerations occur, the backrest of a seat equipped in this way would unavoidably "slide through", i.e. the adjustment fitting could not absorb the large forces and shunt them into the seat frame.
For this reason motor vehicle seats are conventionally built with one adjustment fitting on each seat side. In order to attain synchronous adjustment, the two fittings are coupled with one another through a shaft. In the case of motor vehicle seats integrated with belts, the adjustment fitting on the one seat side where the belt member is integrated into the backrest frame must be implemented especially strong since the retaining forces of the integrated belt carried on the seat must be intercepted in the seat itself, i.e. by its frame construction, which forces are carried off therefrom into the motor vehicle floor. The articulations between the backrest and the seat part represent a substantial member in the chain of diversion of force.
German patent document No. DE-OS 22 38 899 discloses a safety locking mechanism in particular for a reclining seat fitting of a motor vehicle seat. This fitting comprises a first fitting part fixedly disposed on the seat frame and a second fitting part disposed on the seat backrest and articulated with the first fitting part through a pivot axle. Both fitting parts are adjustable relative to one another by means of a latching arrangement. This latching arrangement comprises a pinion, rotatably supported on the first fitting part secured stationarily on the seat frame, which engages an internal teething disposed concentrically to the pivot axis. On the pinion axle extending parallel to the pivot axis and on the second fitting part is seated a toothed wheel which can be locked by an arresting lever. In the locked position, the first and second fitting parts cannot be pivoted toward one another. Also on the pinion axle parallel to the toothed wheel is seated a locking wheel with which is associated at least one locking pawl articulated on the first fitting part secured on the seat frame, which through inertia can be made to engage the locking wheel. Thereby the seat backrest is said to be blocked even with the latching device disengaged during strong accelerations.
The above-described arrangement has several drawbacks. It comprises a relatively large number of structural members and for that reason is disturbance-prone. Furthermore, it is neither suitable for replacing an adjustment fitting on a seat side nor can it be used for reinforcing an adjustment fitting.